California Code, Revenue and Taxation Code - RTC § 862

When an assessee, after a request by the board, fails to file a property statement by the date specified in Section 830 or files with the board a property statement or report on a form prescribed by the board with respect to state-assessed property and the statement fails to report any taxable tangible property information accurately, regardless of whether or not this information is available to the assessee, to the extent that these failures cause the board not to assess the property or to assess it at a lower valuation than it would have if the property information had been reported accurately, the property shall be assessed in accordance with Section 864, and a penalty of 10 percent shall be added to the additional assessment.  If the failure to report or the failure to report accurately is willful or fraudulent, a penalty of 25 percent shall be added to the additional assessment.  If the assessee establishes to the satisfaction of the board that the failure to file an accurate property statement was due to reasonable cause and occurred notwithstanding the exercise of ordinary care and the absence of willful neglect, the board shall order the penalty abated, in whole or in part, provided that the assessee has filed with the board written application for abatement of the penalty within the time prescribed by law for the filing of applications for assessment reductions.